| Mobius Professional Services Limited | Professional & scientific | 2016 |
| Moby's Table Limited | Hospitality | 1998 |
| Mocca Cleaning Services Ltd | Administrative & support | 2023 |
| Modbits Ltd | Other services | 2019 |
| Mode 8 Limited | Construction | 2023 |
| Modern Artbuyer Limited | Wholesale & retail | 2012 |
| Modern Pentathlon Association of Great Britain Limited | Arts & recreation | 2003 |
| Modusnova Ltd | Wholesale & retail | 2015 |
| MOG & Bear Ltd | Professional & scientific | 2017 |
| Mog's Shop Limited | Wholesale & retail | 2023 |
| Mohio Advisory Ltd | Information & communication | 2016 |
| Mohio Investments Limited | Professional & scientific | 2013 |
| Mohio Technology Ltd | Information & communication | 2016 |
| Mojoprint UK Ltd | Manufacturing | 2015 |
| Mokoko Coffee Limited | Extraterritorial | 2017 |
| Mokoko Limited | Extraterritorial | 2017 |
| Molehill Construction Limited | Construction | 2011 |
| Molehill Design Limited | Professional & scientific | 2025 |
| Molehill Properties Ltd | Real estate | 2022 |
| Molehill Waste Clearance Limited | Water & waste | 2016 |
| Momentum Consulting Engineers Limited | Professional & scientific | 2005 |
| Momentum Professional Development Ltd | Professional & scientific | 2021 |
| MON Prestige (UK) Ltd | Wholesale & retail | 2023 |
| Monal Limited | Households | 1984 |
| Monarch Lettings Ltd | Real estate | 2025 |
| Monday Nights Ltd | Professional & scientific | 2022 |
| Mondo Industries Limited | Manufacturing | 2010 |
| Money Wise Independent Financial Advisers Limited | Professional & scientific | 1997 |
| Monkey Doodle Limited | Arts & recreation | 2016 |
| Monkey Island Properties Limited | Real estate | 2015 |
| Monkton Combe School Enterprises Limited | Education | 1998 |
| Monkton International Limited | Education | 2017 |
| Monochrome Digital Ltd | Information & communication | 2024 |
| Monolith Group Limited | Financial services | 2020 |
| Monrroe Ltd | Information & communication | 2024 |
| Montana Healthcare Ltd | Health & social care | 2007 |
| Monte Mansions Management Company Limited | Households | 1983 |
| Montroc Consulting Limited | Professional & scientific | 2018 |
| Montvieux Limited | Information & communication | 2007 |
| Moomalu Ltd | Real estate | 2016 |
| Moonfield Ltd | Wholesale & retail | 2020 |
| Moonshine Books Ltd | Construction | 2021 |
| Moonstone Models Ltd | Administrative & support | 2025 |
| Moore (Holdings) Limited | Professional & scientific | 2013 |
| Moore Yacht Design Ltd | Administrative & support | 2008 |
| Moorhouse PMC Ltd | Households | 2021 |
| MOP MOW & More Limited | Extraterritorial | 2018 |
| Mopane Advisors Limited | Professional & scientific | 2021 |
| Morcom Design Workshop Limited | Professional & scientific | 2011 |
| Moregiftboxes Ltd | Manufacturing | 2021 |
| Moresoda Design Ltd | Information & communication | 2007 |
| Moreton Landscape Architecture Limited | Professional & scientific | 2019 |
| Morgan Financial Group Holdings Limited | Professional & scientific | 2012 |
| Morgan Financial Group Ltd | Financial services | 1992 |
| Morris & Co Surveyors Limited | Real estate | 2014 |
| Morrison Studios Chartered Architects Ltd | Professional & scientific | 2024 |
| Morso Vegan Ltd | Hospitality | 2023 |
| Mortgage Gold Ltd | Financial services | 2021 |
| Moss Works Ltd | Construction | 2023 |
| Mostly Media Limited | Professional & scientific | 1994 |
| Mostlywanted Limited | Arts & recreation | 2004 |
| Mothership Consultants Limited | Information & communication | 1997 |
| Motionless Horizon Holdings Limited | Financial services | 2021 |
| MOTIV8 Career Services Ltd | Education | 2025 |
| Motojourney Limited | Wholesale & retail | 2024 |
| Motor Village Bristol Ltd | Wholesale & retail | 2019 |
| Motorcap Ltd | Wholesale & retail | 2024 |
| Motrinsic Limited | Professional & scientific | 2021 |
| Mount Haviland Limited | Households | 2019 |
| Move Mountains Coaching Ltd | Professional & scientific | 2025 |
| Move Technologies Group Ltd | Information & communication | 2022 |
| Movie Mogul Ltd | Information & communication | 2004 |
| Mowat Velo Limited | Wholesale & retail | 2025 |
| MP Bath LLP | | 2024 |
| Mptac Ltd | Information & communication | 2026 |
| MR B'S Emporium Limited | Wholesale & retail | 2000 |
| MR Control Ltd. | Information & communication | 1999 |
| MR DS Bath Ltd | Hospitality | 2025 |
| MR P. Studios (UK) Limited | Professional & scientific | 2026 |
| MR P. Studios Group Limited | Financial services | 2026 |
| MR-C187 Ltd | Financial services | 2025 |
| Mr.Willats' Corporate Trustee Limited | Other services | 2013 |
| Mrca Limited | Other services | 2026 |
| Mrhd Consulting Ltd | Professional & scientific | 2015 |
| Mrpc Bristol Computer Services Limited | Other services | 2023 |
| MS Dalton Ltd | Real estate | 2014 |
| Msquared Consulting Ltd | Other services | 2018 |
| MTP Orthopaedic Limited | Health & social care | 2013 |
| Mtpredictor Limited | Information & communication | 2003 |
| MTS Coaching Ltd | Education | 2024 |
| MTS Precision Limited | Manufacturing | 1996 |
| Mudlark Sound Studios Limited | Information & communication | 2014 |
| Muirmacdonald.Com Limited | Professional & scientific | 2018 |
| Mulberry Garden Nursery and Preschool Ltd | Education | 2022 |
| Mulberry Group Holding Company Limited | Financial services | 2018 |
| Mulberry Trading Holding Company Limited | Financial services | 2018 |
| Mulhouse Global Limited | Hospitality | 2021 |
| Multi Diving Services Ltd | Professional & scientific | 2024 |
| Multi Water Solutions Ltd | Transport & logistics | 2023 |
| Mum-Dance London Ltd | Arts & recreation | 2024 |